Pallikara Ioanna, Skelton Jonathan M
Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
Phys Chem Chem Phys. 2021 Sep 15;23(35):19219-19236. doi: 10.1039/d1cp02597j.
The tin monochalcogenides SnS and SnSe adopt four different crystal structures, orthorhombic and and cubic rocksalt and π-cubic (23) phases, each of which has optimal properties for a range of potential applications. This rich phase space makes it challenging to identify the conditions under which the different phases are obtained. We have performed first-principles quasi-harmonic lattice-dynamics calculations to assess the relative stabilities of the four phases of SnS and SnSe. We investigate dynamical stability through the presence or absence of imaginary modes in the phonon dispersion curves, and we compute Helmholtz and Gibbs free energies to evaluate the thermodynamic stability. We also consider applied pressures up to 15 GPa to obtain simulated temperature-pressure phase diagrams. Finally, the relationships between the orthorhombic crystal phases are investigated by explicitly mapping the potential-energy surfaces along the imaginary harmonic phonon modes in the phase, and the relationships between the cubic phases are found by transition-state modelling using the climbing-image nudged elastic-band method.
一硫化锡和硒化锡采用四种不同的晶体结构，即正交晶系、立方岩盐结构和π立方（23）相，每种结构在一系列潜在应用中都具有最佳性能。这种丰富的相空间使得确定获得不同相的条件具有挑战性。我们进行了第一性原理准谐晶格动力学计算，以评估一硫化锡和硒化锡四个相的相对稳定性。我们通过声子色散曲线中虚模的有无来研究动力学稳定性，并计算亥姆霍兹自由能和吉布斯自由能以评估热力学稳定性。我们还考虑了高达15吉帕的外加压力，以获得模拟的温度-压力相图。最后，通过沿正交晶相中的虚谐声子模明确绘制势能面来研究正交晶相之间的关系，并使用爬坡图像推挤弹性带方法通过过渡态建模来确定立方相之间的关系。
